Effect of annealing on optical and structural properties of ZnS/MnS and MnS/ZnS superlattices thin films for solar energy application

ZnS/MnS super lattice thin films were grown on glass substrates by Chemical Bath Deposition technique. Equimolar aqueous solutions of ZnCl2:thiourea and MnCl2·2H2O:thiourea were taken separately. The substrates were placed vertically in the beakers containing the precursor described above, and the films are deposited at 85 °C for an hour. The as deposited films are annealed at 200 °C for about two hours. X-ray diffractometry method was used to obtain structural characterization. The UV–vis absorption spectrometry was employed to find the optical properties. The refractive-index, dielectric constant, optical conductivity, electrical conductivity and extinction coefficient were determined by various equations based on the data. The valence band and conduction band offset voltages for ZnS/MnS were determined as 0.7 eV and 0.1 eV respectively and for MnS/ZnS were 0.4 eV and 0.3 eV respectively. The band alignment of both superlattice was found to be as Type I.